1. Field of the Invention
The invention relates generally to aircraft flight recorders that employ solid state memory devices in memory means used to store flight data. More particularly, the invention relates to methods and apparatus for reducing the memory volume required for housing a solid state recording device so that the volume reduction can be advantageously used in other ways, such as to increase insulation thickness for improved fire protection, decrease crash housing size for weight reduction and improved crash protection, etc.
2. Description of the Related Art
Aircraft flight recorders, such as those installed aboard civilian and/or military aircraft, are commonly used to collect essential data of flights in progress and to record data of one or more flights for eventual read-out.
Such read-out may take place for an eventless flight. Unfortunately, it may also be necessary to read out recorded flight data in case of a possibly serious accident. The later eventuality requires that the flight recorder be able to meet adverse survival requirements designed to insure that the memory survives the possibility of extreme temperatures, pressures, shock, the effects of corrosion, etc., that the flight recorder may be exposed to as a result of an aircraft accident.
Problems related to the survivability of flight recorders have been addressed by the prior art. For example, flight recorders that used magnetic tape as a recording medium and further contained moving magnetic parts for writing data to such tapes, etc., have been replaced with solid state memory devices that eliminate moving parts and provide a more reliable means of preserving recorded data. Furthermore, prior art electronic device packages are known (for flight recorders and other devices as well) in which solid state memory cards are stacked to conserve space, to reduce package density with the object of reducing overall device package size, etc.
An example of one such device in the flight recorder context is described in U.S. Pat. No. 5,053,967, issued Oct. 1, 1991, to Clavelloux et al. In particular, the 5,053,967 patent, hereby incorporated by reference, describes a solid state memory device that uses EEPROM type memory chips on stacked memory cards to record flight data.
According to the incorporated reference, the EEPROM based memory circuits are sealed in metal cases. The metal cases are filled with an incompressible inert liquid to eliminate voids to make the packages pressure resistant. Circuit cards, on which circuits containing the scaled memory chips are included, are stacked and braced inside a housing, using glass micro balls to wedge the circuit cards therein.
The incorporated reference further teaches separating the stacked cards with spacers; stacking the memory cards so that they assume a parallelepiped shape in the memory housing; interconnecting the edges of the stacked cards using flexible circuits; and preferably protecting all input connections toward the memory means in parallel by using fast unidirectional zener diodes.
Further yet, the incorporated reference teaches using a silicon based anti-corrosion product, applied to both sides of the printed circuit board or cards so that the circuit cards are at least temporarily resistant to fire and deep sea immersion.
Although describing a flight recorder that includes solid state memory devices (the EEPROM chips) on stacked circuit boards, etc.; the teachings of the incorporated reference would make it difficult, if not impossible, to realize levels of memory module packaging density desirable (and in many cases required) for present day aircraft flight recorders.
Reasons why the teachings of the incorporated reference are inherently problematic include:
(1) The EEPROM type memory required by the incorporated reference is not dense enough to facilitate high density packaging; particularly when compared with the density of other present day commercially available non-volatile memory devices, such as flash memory chips, etc. PA1 (2) The means used to facilitate the stacking of cards taught in the incorporated reference (card edge connectors) are themselves one of the most significant contributors to increased package size since, as those skilled in the art will readily appreciate, the connectors are typically the largest element on the circuit board. The problem is compounded as the number of connector; and/or number of interconnected stacked boards goes up (i.e., where a large number of connectors are used) and will itself have a direct negative impact on board size and overall package density. The problem is compounded even further by any requirement that all such connectors have to be located on the edge of each card, as taught by the incorporated reference.
Other inherent problems stemming from the teachings of the incorporated reference include: (a) the manufacturing process steps required to fill voids in the metal IC packages with the incompressible liquid; (b) the difficulty of insuring the stacked cards are properly wedged in the memory module housing particularly when, as taught in the incorporated reference, components are braced inside the housing using foreign objects, like glass micro balls, to wedge the circuit cards therein; (c) the problems that can arise from the wide temperature range over which the memory module must operate, particularly when the package contains a wide variety of internal materials such as glass (the micro balls), plastics, liquids, etc.; (d) the problems associated with insuring a uniform coat of the silicon based anti-corrosion product called for by the incorporated reference, the ability of silicon to perform well as an anti-corrosion product in the extreme temperature environments that the memory module may be exposed to, etc.; (e) the use of the extra components and manufacturing process steps suggested by the incorporated reference in order to protect all input connections toward the memory means in parallel (not necessary in many cases).
In view of the above, it would, for example, be desirable to provide a flight recorder that includes a memory module that contains printed circuit boards (where the term "printed circuit board" is defined herein to include unassembled printed circuit cards and printed circuit boards that are fully assembled, sometimes described more particularly as a "printed wiring assembly", with these terms all being used interchangeably herein), which allow interboard connectors to be located any place on the board (i.e., not just at the board edges; but anywhere else on and within the perimeter of the board) to help improve overall flight recorder memory module packaging density.
It would be further desirable to provide a flight recorder, flight recorder memory module and flight recorder memory module manufacturing process that solves the other problems discussed hereinabove.
Other patented examples of circuit packaging techniques in general, memory module packaging techniques, etc., that illustrate the present state of the art include: U.S. Pat. Nos. 5,412,538, issued May 2, 1995, to Kikinis et al.; 4,833,568, issued May 23, 1989, to Berhold; 4,574,331, issued Mar. 4, 1986, to Smolley; 5,251,099, issued Oct. 5, 1993, to Goss et al.; 4,953,005, issued Aug. 28, 1990, to Carlson et al.; 4,520,427, issued May 28, 1985, to Brotherton et al.; and Japanese Patent 59-205747, issued Nov. 21, 1984, to Kondou.
Multi-dimensional and multi-element electronic packaging techniques; as well as space saving memory module packaging techniques per se, are taught in the 538' patent to Kikinis et al. (directed to space saving memory modules); the 568' patent to Berhold (directed to three-dimensional circuit component assemblies and methods for constructing such assemblies); and the 331' patent to Smolley (directed to multi-element circuit construction).
Both the 568' and 331' patents, like the incorporated reference, require that the electrical connections between boards be on the board edges; again, this factor adversely affecting the potential for increasing package density for the reasons stated hereinbefore.
The 538' patent requires through hole connections that involve extra process steps during module fabrication (machining steps). Furthermore, as those skilled in the art will readily appreciate, package density is adversely affected by using through hole connectors as taught by the 538' reference.
Accordingly, it would be desirable, in addition to the other desired features of the invention discussed hereinabove, to be able to provide a flight recorder that does not require the use of through hole connectors or edge connections between printer circuit boards to thereby eliminate at least two of the difficulties in achieving increased package densities, reduced memory module sizes, etc.
The 099' patent to Goss et al., describes a high density electronics package that houses a plurality of circuit cards, heat sinks and circuit interconnections in a single conical shaped housing. The package includes stacked circuit boards.
According to the teachings of the 099' patent, connectors and connector pins on pairs of adjacent boards are interconnected through an opening in a heat sink disposed between the boards; and subassembled pairs of boards are interconnected directly to one to another (again using connectors and connector pins) without the use of an intervening heat sink, to form the card stack assembly located within the conical assembly. The card stack is locked in the housing using a multi-components locking mechanism (including tapered lock rings, screws and locks) to force the circuit boards, heat sinks and electrical connections contained within the housing, against the inner housing wall to secure the components placed therein.
Those skilled in the art will readily appreciate, using the teachings of the 099' patent as a point of reference, that it would be desirable to provide a high density package for a solid state flight recorder memory that does not require the use of heat sinks, conic surfaces, intricate locking mechanisms or require connector pins for making electrical connections between boards in the package.
Realizing this desire would eliminate such problems as having of having to drill holes in boards to affix the connectors and pins; reduce board to board spacing requirements necessitated by the size and bulk of such connectors and pins (which when used result in larger volume package requirements); and minimize the number of components required within the housing (for example, the aforementioned locks, tapered rings, screws, heat sinks, etc). It should be noted that in some applications it may be desirable to include heat sinks within the memory module package; however, the need for such devices within the memory module per se could be reduced and even eliminated entirely if memory module packaging size is reduced to the point where the memory module can be adequately protected from heat by insulation located outside the memory module per se (for example, insulation contained within the flight recorder; but located outside and surrounding the desired densely packed memory module included in the flight recorder).
The 005' patent to Carlson et al., describes a packaging system for stacking integrated circuits to provide short interconnection paths between such circuits.
According to the teachings of the 005' patent, integrated circuit dies are mounted to the interconnection leads on frames of tape automatic bonding (TAB) film. Thereafter, each frame of the TAB film with the attached integrated circuit die is affixed to an electrically insulating, thermally conductive plate to form a sandwich structure.
A number of sandwich structures are bonded together to form a stack of sandwiches (i.e., multiple layers of semiconductor devices and spacers assembled in a stack) which are secured together by tie use of rods. The interconnection leads of each sandwich is made on a common outer surface with conductors. The multi-layer assembly, which could be cylindrically shaped or the shape of a square, etc., is then placed in a housing.
Those skilled in the art will readily appreciate that the packaging techniques taught in the 005' patent are not readily adaptable for use in the flight recorder context for several reasons. First, unit serviceability would be very difficult. To get to the surfaces of a given sandwiched structure, the bonded structures would need to be taken apart. Since the integrated circuit dies are mounted to the interconnection leads on frames of film; and the interconnection leads of each sandwich is then made on a common outer surface with conductors, if one layer suffers a failure it would be necessary to break all vertical conductors to disassemble and repair a layer, etc.
Accordingly, it would be desirable to provide a flight recorder and memory module therefore, that is easy to assemble, disassemble and service.
The 427' patent to Brotherton et al. teaches an electrical assembly that includes a stack of modules secured in a bore through a casing. All connections between boards (which are circular) are made on the periphery of the boards. The 427' patent goes on to teach that the component casing includes longitudinal grooves on the internal surface thereof for accommodating electrical interconnections between modules, insulating material, etc. The multiple modules are secured by using rods and then the whole assembly is placed in a cylindrical housing.
Although the 427' patent represents an improvement over the edge connection strategies discussed hereinbefore with reference to, for example, the incorporated reference (though the 427' patent is not directed to flight recorder memory modules per se); the 427' patent still requires that: connections between boards be made on the periphery thereof. Accordingly, connector density maximization prospects are again limited when compared with a desirable strategy that would allow a connector to be located any place on the board.
Additionally, the machining steps required to manufacture the type of casing called for by the 427' patent (i.e., machining a casing that includes longitudinal grooves on its internal surface to accommodate electrical interconnections between modules, insulating material, etc.), are time consuming and costly.
It would be desirable to be able to produce high density flight recorder memory modules without having to perform such machining operations. Still further, the teachings of the 427' patent require the handling and manipulation of many loose pieces during the assembly process (for example, the conductive members depicted in FIG. 1 of the 427' patent, etc.), which for obvious reasons is not desirable.
Finally, the aforementioned Japanese Patent to Kondou (patent number 59-205747), discloses techniques for manufacturing a semiconductor device taking the form of multiple layer assemblies bonded together with a heat resisting resin. Alternate spacers and stacked substrates are used. Space formed by the spacers is filled with an insulating adhesive resin, such as epoxy; and the resin is cured. Interconnections between layers is made via edge connecting a set of exposed electrode terminals, exposed to the side surface of the device.
The packaging techniques taught in Japanese Patent 59-205747 to Kondou require bonding multiple assembly layers together which, as indicated hereinbefore, is problematic when trying to effect repairs on assembly components without destroying the assembly. The packaging process taught by Kondou also requires the application of heat as part of the manufacturing process.
In the flight recorder memory module context, where thermal expansion and pressure problems need to be anticipated and dealt with, bonding assemblies together and filling spaces between stacked circuits with an insulating adhesive resin (as taught by Kondou) would only compound the number of variables that need to be addressed in order to protect the module under adverse temperature and pressure conditions.
Still further, the teachings of Kondou (employed at the sub-chip level, working with dies; as opposed to dealing with the packaging of memory chips in a flight recorder memory module environment at the circuit board level), call for interconnections between layers to be made via edge connecting a set of exposed electrode terminals (exposed to the side surface of the device), which if applied at the circuit board level (for the reasons stated hereinbefore) would not lend itself to increasing connector density and overall package density.
Accordingly, it would be desirable to provide a flight recorder, flight recorder memory module and flight recorder memory module fabrication techniques that do not require the steps of bonding components or assemblies together; do not require the use of heat or filling spaces between stacked circuit cards with resins or any other material that needs to be cured, during the assembly process; or require using edge connections to interconnect layers of stacked circuitry.
In addition to all of the aforementioned desirable attributes of flight recorders, flight recorder memory modules and flight recorder memory module fabrication techniques, it would be desirable to reduce the memory volume required for a solid state flight recorder so that the volume saved could, as indicated hereinbefore, be used in other ways, such as to increase insulation thickness for improved fire protection; decrease crash housing size for weight reduction and improved crash protection, etc.